Preparation of naphthalene and certain dimethylnaphthalenes



United States Patent 3,235,615 PREPARATION OF NAPHTHALENE AND CERTAIN DIMETHYLNAPHTHALENES Joseph G. Allen, Ridley Park, Pa., and Earl W. Malmberg,

Wilmington, Del.,, assignors to Sun Oil Company,

Philadelphia, Pa., a corporation of New Jersey Filed Oct. 10, 1961, Ser. No. 144,197 7 Claims. (Cl. 260-668) This invention relates to the preparation of condensed ring dicyclic aromatic hydrocarbons from charge stocks derived from gas oil and more specifically concerns an integrated process for producing naphthalene and 2,3-, 2,6- and 2,7-dimethylnaphthalenes.

Petroleum fractions which boil within the range of 400-550 F. generally contain substantial amounts of alkylnaphthalenes, such as mono-, diand trimethy1- naphthalenes and in smaller quantity, the ethylnaphthalenes. Recycle fractions, which are formed in the cracking of petroleum stocks and which include this boiling range, often contain major proportions of aromatic hydrocarbons that are mainly alkylnaphthalenes. Such fractions typically may have aromatic contents varying within the range of 2597% but usually contain between 50% and 95% aromatics depending upon the particular operation in which the petroleum fractions are produced. These hydrocarbon charge stocks are obtained in both catalytic and thermal cracking processes and in operations in which combinations of catalytic and thermal cracking steps are utilized. Stocks having high alkylnaphthalene contents can also be obtained by extracting straight run petroleum fractions of appropriate boiling ranges, such as kerosene, or catalytic fractions such as catalytic gas oil, with solvents, such as furfural or sulfur dioxide, or by selective adsorption with silica gel. These aromatic con centrates may contain up to 100% aromatic hydrocarbons.

The present invention is directed to the preparation of naphthalene and also the 2,3-, 2,6- and 2,7-dimethylnaphthalenes from aromatic hydrocarbon charge stocks which comprise a mixture of alkylnaphthalenes and which can be derived from such sources as referred to above. The charge stock typically includes the two monomethylnaphthalenes, various dimethylnaphthalene isomers and smaller amounts of the ethylnaphthalenes.

There are ten possible dimethylnaphthalene isomers and most if not all of these occur in charge stocks of the kind describedabove. Due to the close boiling points of these isomers, the separation from the mixture of any particular isomer in high concentration is a diflicult task. Suitable procedures for obtaining individual isomers from such charge stocks are particularly desirable, since the isomers can serve as intermediates in the preparation of other useful products such as high quality resins. The present invention provides an integrated process for obtaining the 2,3-, 2,6- and 2,7-isomers, while simultaneously converting other alkylnaphthalenes to naphthalene. For convenience the dimethylnaphthalenes are sometimes herein referred to as DMN.

In one embodiment of the invention an aromatic concentrate of the 440520 F. boiling range, containing mainly monocyclic and dicyclic aromatic hydrocarbons, is subjected to a pre-conditioning step involving hydrodesulfurization under conditions whereby sulfur is removed and the monocyclic aromatics largely are cracked to gasoline boiling range products. From the desulfurization product three fractions having approximate boiling ranges, respectively, of 500-509 F., 509-5 13 F. and 513520 F. are obtained by distillation under efiicient fractionating conditions. We have found that the 500- 509 P. fraction contains most of the 2,6- and 2,7-DMN present in the charge, together with substantial amounts 3,235,615 Patented Feb. 15, 1966 of 1,3-, 1,6- and 1,7-DMN and a small amount of ethylnaphthalenes. The 513520 F. fraction contains most of the 2,3-DMN, the other constituents mainly being isomers having a methyl group in the 1-position. The intermediate fraction is largely composed of isomers having a methyl group in the 1-position but it also contains the 2,3-, 2,6- and 2,7-isomers in relatively small amounts. The SOD-509 F. and 513520 -F. fractions are subjected to separate crystallization operations to obtain 2,6- and 2,7-DMN from the lower boiling fraction and 2,3-DMN from the higher boiling fraction. The intermediate fraction, together with filtrates from the two crystallization steps, is subjected to isomerization to produce more of the 2,6-, 2,7- and 2,3-isomers, and the isomerizate is recycled back to the aforementioned distillation step. The material from the distillation step which boils below 500 F. and which is composed largely of methylnaphthalenes together with smaller proportions of ethylnaphthalenes passes to a high temperature dealkylation zone to produce naphthalene. Also a portion of the filtrate from the 2,3-DMN crystallization step preferably is sent to the dealkylation zone to prevent the buildup of 1,2-DMN in the system as hereinafter more fully explained.

The invention is described more specifically with reference to the accompanying drawing which is a schematic flowsheet illustrating a combination process for producing naphthalene and the 2,3-, 2,6- and 2,7-dimethylnaphthalenes from a hydrocarbon stock containing alkylnaphthalenes.

The process as illustrated in the drawing involves a preliminary extraction step followed by a catalytic hydrocracking-desulfurization step adapted to condition the alkylnaphthalene charge material for use in the other steps of the process. The charge, which enters the system through line 10, is a gas oil fraction boiling in the approximate range of 440-520 F. and containing alkylnaphthalenes including monomethylnaphthalenes and di methylnaphthalenes together with saturated hydrocarbons. It is fed to extractor 11 wherein it is countercurrently extracted with an aromatic-selective solvent, which preferably is furfural, under conditions that will produce a highly aromatic extract. Rafiinate, which includes the bulk of the saturated hydrocarbons and part of the monocyclic aromatics, is removed as indicated by line 12, and extract is withdrawn via line 13. Conventional solvent separation means (not shown) are provided for recovering and recycling the solvent. The extract obtained from this step typically may contain about-60'65% dicyclic aromatics, 35% monocyclic aromatics and 05% saturates. Y

The heated extract, together with hydrogen from line 14, passes through line 15 to a catalytic desulfurizerhydrocracker 16 which contains a desulfurization catalyst such as cobalt molybdate on alumina or molybdenum disulfide on alumina. The conditions for conducting this catalytic conditioning step include a temperature within the range of 800980 F., a pressure of 15-1000 p.s.i.g., with a range of 200-500 p.s.i.g. preferred, a hydrogen to hydrocarbon mole ratio of 3:1 to 25:1 and preferably 5:1 to 15:1, and a liquid hourly space velocity of 0.5 to 10 (volumes of charge per hour per bulk volume of catalyst). The hydrogen consumption under these conditions should be between 65500 s.c.f. per barrel of liquid feed per percent sulfur in the feed and preferably between 200 and 400 s.c.f. per barrel. This conditioning step effects cracking of most of the saturates and some of the monocyclic aromatics and also converts most of the sulfur in the hydrocarbon stock to hydrogen sulfide.

From hydrocracker 16 the reaction product is sent through line 17 to fractionator 18 from which normally gaseous components are removed ove-rhead through line 19 and a (l -400 F. gasoline fraction is obtained from line 20. The 400+ P. fraction which contains the alkylnaphthalenes is removed via line 21 and passes to a fractionation section (hereinafter described) for separation into a 400-500. P. fraction and the three narrow fractions previously specified.

Referring now to the high temperature dealkylation step for producing naphthalene, a stream of mixed materials, obtained as hereinafter specified and composed mainly of monomethylnaphthalenes together with small amounts of ethylnaphthalenes and dimethylnaphthalenes, passes through. line 22 together with hydrogen introduced via line 23 into dealkylator 24. In one embodiment the dealkylation is effected thermally without a catalyst. The conditions for this operation include a pressure of 150- 1000 p.s.i.g., preferably 200-500 p.s.i.g., a hydrogen to hydrocarbon mole ratio within the range of 3:1 to 25 :1 and preferably :1 to :1, a residence time of 2-300 seconds with a preferred residence time of 10-60 seconds, and a temperature above 1000 F., preferably within the range of l200-1400 F., Sllfi'lCl6Hf to effect dealkylation of alky-lnaphthalenes. In this reaction only a partial dealkylation occurs. Hence the reaction product which leaves the reactor through line 25 contains, in addition to the desired naphthalene, unreacted naphthalenes and partially dealkylated naphthalenes which can be recovered and recycled to the dealkylator.

Alternatively, the dealkylation reaction can be effected catalytically utilizing a desulfurizing catalyst such as cobalt molybdate or molybdenum disulfide. The presence of the catalyst in this step facilitates the deali tylation reaction and in some cases permits it to be carried out at a lower temperature than that required for thermal dealkyl-ation. The catalyst also effects the conversion of any remaining sulfur into hydrogen sulfide and hence permits the preparation of naphthalene having negligible sulfur content. The conditions for the catalytic dealkylation step include a pressure of 150-1000 p.s.i.g. with a range of 200-500 p.s.i.g. preferred, a hydrogen to hydrocarbon mole ratio of 5:1 to 25:1, a liquid hourly space velocity of 0.2-5.0, and a temperature above 1000 F., usually between 1100 F. and 1200 F., sufficient to dealkylate alkylnaphthalenes and convert any remaining sulfur mainly into hydrogen sulfide.

The reaction product from line 25 passes to a fractionating zone, illustrated as 26, from which gases and a C -400 F. aromatic gasoline out are removed, respectively, from lines 27 and 28. The desired naphthalene product is taken from line 29 as material boiling in the 400-450" F. range. Typically this fraction is composed predominantly of naphthalene and has a freezing point of 78.6 C. and a sulfur content that is practically negligible. A fraction boiling in the range of 450-520 F. is withdrawn from fractionator 26 via line 30. This fraction comprises unconverted and partially converted alkylnaphthalenes and is recycled through line 22 to dealkylator 24 for further conversion. Material boiling above dimethylnaphthalenes which forms to some extent during the dealkylation reaction is obtained as residuum from fractionating zone 26 and is removed from the process via line 31.

Referring now to the portion of the process for obtaintaining the 2,3-, 2,6- and 2,7-DMNs, the 400+ F. fraction of the desulfurization product passes through lines 21 and 33 to a fractionating section illustrated by the three distillation columns 34-, 35 and 36. Each of these distillation columns should be operated under efiicient fractionating conditions employing, for example, 30-50 theoretical plates and reflux ratios'of the order of 30:1 to 50: 1. In column 34 all of the material boiling below 500 Ftisdistilled overhead, from where it passes through lines 37 and 22 to the dealkylator 24. The 500+ P. fraction from column 34 passes through line 38 to column 3-5 and is therein sharply fractionated to obtain through overhead line 39 the fraction which. boils approximately in the range of 500509 F. The residue from column 35 is sent through line 40 to column 36 from which the narrow boiling 509-513 P. fraction is obtained through overhead line 41 and the 513-520 F. bottoms fraction is Withdrawn via line 42. V

The 500-509 F. cut from column 34 will contain a major proportion of dimethylnaphthalenes having the methyl groups on opposite rings of the naphthalene nucleus, minor proportions of ethylnaphthalenes and 1,3- DMN and substantially no 2,3-DMN. A typical composition of this material is as follows:

2 Dimethylnaphthalene.

This material is sent through line 39 to a crystallizing and filtering zone 43 wherein the material is chilled to a temperature preferably in the range of 0-30 F. and is filtered at such temperature. This tends preferentially to crystallize the 2,6- and 2,7-DMN and gives a filtrate from line 44- Which contains other components of the feed to the crystallizer together with part of the 2,6- and 2,7- DMN present in the feed.

The filter cake obtained as indicated by line 45 is composed mainly of 2,6- and 2,7-DMN, and if desired it can be subjected to a partial melting in zone 46 to separate these components from each other. This can be done by warming the cake to a temperature preferably of about 70-85 F. While preming it to squeeze out the melted material which is filtered off through line 47. It has been found that this procedure will give a residual filter cake, indicated by line 48, which has a 2,6-DMN content of the order of -95% and which. contains about 25-35% of the 2,6-DMN that was present in the material fed to zone 46. The filtrate from line 47 is enriched with respect to 2,7-DMN but also contains a substantial proportion of the 2,6-isomer. This filtrate can, if desired, be subjected to another crystallization and fractional melting operation (not shown) to effect further separation of these components. Alternatively, if 2,7-DMN is not desired as a separate product of the process, the filtrate can be sent (by means not shown) to dealkylator 24 for conversion to naphthalene.

The 513-520 P. fraction from tower 36 will contain substantially no 2,6- and 2,7-DMN. and typically may have the following composition:

Percent 1,3-DMN 13 1,7-DMN 7 1,6-DMN 19 2,3-DMN 48 1,4-DMN 1 1,5-DMN 8 1,2-DMN 7 1,8-DMN 7 It is to be noted that approximately one-half of this fraction is the 2,3-isomer. This material is passed through line 42 to a crystallization-filtration operation, indicated at 48, for recovering the 2,3-DMN in high purity. One suitable procedure for obtaining this product comprises crystallizing at a temperature in the range of l0 to +20 C., e.g., at about 0 C., pressing the filter cake at the same temperature to squeeze out the filtrate, dissolving the cake in methanol and then recrystallizing. We have found that by such procedure about one-fourth or more of the 2,3-DMN in the feed to the crystallizer can be recovered, as indicated by line 49, in surprisingly high purity, e.g., 98-100%-. The non-recovered 2,3-DMN will be present in the filtrate obtained from this operation through line 50.

. The 509513 F. fraction obtained from tower 36 is composed predominantly of the 1,3- and 1,6-isomers and it usually contains of the order of 5-10% each of 2,6- DMN, 2,' /-DMN and 2,3-DMN. Only small amounts of the 1,4- and 1,5-isomers appear in this cut and it generally contains practically no 1,2-DMN and 1,8-DMN. This material is sent through line 41 to line 51 where it is admixed with the filtrate from line 44 and the other filtrate from lines 50 and 53, and the mixture is sent to an isomerization zone 52 wherein it is subjected to conditions effectiveto cause-a shift in position of methyl groups, whereby further amounts of the 2,3-, 2,6- and 2,7-DMN isomers are formed. --A procedure for carrying out such isomerization reaction has been described in Seitzer application United States SerialNo.28,753-, filed May 12, 1960, now abandoned. It involves contacting the alkylnaphthalenes with any solid acidic cracking catalyst such as silicaalumina, silica-magnesia, silica-zirconia and acid activated clays. The reaction temperature should be in the range of 300500 C. and more preferably 325400 C. The liquid space velocity can vary between 0.1 and 20 volumes hydrocarbon per volume catalyst per hour and more preferably is maintained in the range of 0.56.0. It is desirable to conduct the isomerization at a low hydrocarbon partial pressure and generally in the range of ODS-0.5 atmosphere, as otherwise coking tends to occur rapidly with resultant deactivation of the catalyst. The low partial pressure can be maintained either by holding a vacuum in isomerization zone 52 or by introducing an inert diluent along with hydrocarbons, for example, nitrogen, hydrogen, methane, propane, butanes, and the like. Whenever the activity of the catalyst has dropped enough to require regeneration, this can be done in conventional manner merely by blowing air through the hot catalyst to burn off the coke deposits. Thereafter the catalyst can be re-used for further isomerization.

Alternatively, the isomerization in zone 52 can be effected at low temperature using HF-BF as catalyst. In practicing the isomerization in this manner, the alkylnaphthalenes from line 51 are first dissolved in a suitable solvent, such as benzene or heptane, and the mixture is con tacted with the catalyst at a temperature preferably in the range of 30 C. and generally for several hours. Only a small amount of BF need be used and the HF can be present in a large molar excess over the BF to provide sufi'icient catalyst volume for good contact. After the isomerization the solvent can be removed by distillation (not shown). Generally, some amount of tarry material may be formed during this type of isomerizing operation and it also can be removed by distillation.

Following the isomerization reaction the isomerizate is passed through line 53 to line 33 where it mixes with the 400-520 Fehydrodesulfurization product and is then fractionated along therewith to produce the three narrow boiling fractionspreviously described. Thus all of the DMN isomers, with the exception of 1,2-DMN as discussed below, serve as source material for the 2,3-, 2,6- and 2,'7-isomers that can be produced in the process.

By either of the above-described procedures for etlecting isomerization, each of the three desired isomers, viz., 2,3-DMN, 2,6-DMN and 2,7-DMN are formed from other isomers in concentrations dictated by certain equilibria that obtain among the various dimethylnaphthalenes. However it appears that 1,2-DMN is not involved in these equilibria and that it does not undergo isomerization. For this reason, if all the filtrate from crystallizer 48 were sent to isomerizer 52, the 1,2-DMN would tend to build up in the system and its concentrations in the l3520 F. in line 42 and in the filtrate in line 50 would progressively increase. This could be tolerated for a time, since the concentration of this particular isomer in the charge to the process generally is relatively low.

However, provision is made in the present process as illustrated in the drawing for preventing the build up of 1,2-DMN in the system. The stream in which it reaches its highest concentration is in the filtrate that passes from crystallizer 48 through line 50. Accordingly, by sending only a portion of this filtrate to the isomerizer 52 and passing the rest of it through lines 30 and 22 to de alkylator 24, build up of the 1,2-DMN concentration in the system can be avoided. The 1,2-DMN and the other isomers associated therewith in the portion of filtrate sent to the dealkylator serve as additional source material for producing naphthalene. 7

From the foregoing description it can be seen that essentially all of the alkylnaphthalenes present in the charge are utilized to produce either naphthalene, 2,3- DMN, 2,6-DMN, or 2,7-DMN as the chemical products of the process. In addition the process produces gasoline which is highly aromatic and hence has a high antiknock rating.

Iclaima p p 1. Process for producing 2,3-, 2,6- and 2,7 dimethylnaphthalenes from a hydrodesulfurized gas oil aromatic concentrate including aromatics boiling in the range of 500520 F. which comprises: (1) distilling said concentrate to obtain three fractions boiling, respectively, in the approximate ranges of 500-509 F., 509513 F. and 513520 F.; (2) chilling the 500509 F. fraction to a temperature sufliciently low to crystallize 2,6- and 2,7- dimethylnaphthalenes contained therein; (3) separating filtrate from the crystallized product; (4) chilling the 513520 F. fraction to a temperature sufficiently low to crystallize 2,3-dimethylnaphthalene contained therein; (5) separating filtrate from the crystallized 2,3-dimethylnaphthalene; (6) isomerizing the 509-513 F. fraction and filtrates from steps (3) and (5) to form additional quantities of 2,3-, 2,6- and 2,7-dimethylnaphthalenes; and (7) recycling the isomerizate to step (1) for fractionation together with said concentrate.

2. Process according to claim 1 wherein the temperature in step (2) is in the range of 030 C.

3. Process according to claim 1 wherein the crystallized product from step (3) is fractionally melted to obtain a 2,7-dimethylnaphthalene concentrate and a 2,6-dimethylnaphthalene concentrate.

4. Process according to claim 3 wherein the temperature in step (2) is in the range of 030 C. and the fractional melting is effected by increasing the temperature to 85 c.

5. Process according to claim 1 wherein the tempera ture in step (4) is in the range of 10 to +20 C.

6. In a process involving hydrodesulfurizing a gas oil fraction boiling mainly in the range of 440520 F. and containing mainly monocyclic and dicyclic aromatic hydrocarbons including monomethyl and dimethylnaphthale'ne, separating from the desulfurization product material containing alkylnaphthalene and subjecting such material to a dealkylation reaction at a temperature above 1000 F. to produce naphthalene, the steps for recovering 2,3-, 2,'6 and 2,7-dimethylnaphthalenes as additional products which comprises: (1) distilling said desulfurization product to obtain three fractions boiling, respectively, in the approximate ranges of 500-509" R, 509-513 F. and 513-520 F.; (2) chilling the 500509 F. fraction to a temperature sufiiciently low to crystallize 2,6- and 2,7-dimethylnaphthalenes contained therein; (3) separating filtrate from the crystallized product; (4) chilling the 513-520 F. fraction to a temperature sufficiently low to crystallize 2,3-dimethylnaphthalene contained therein; (5) separating filtrate from the crystallized 2,3-dimethylnaphthalene; (6) subjecting said 509413 F. fraction together with filtrate from step (5) and the filtrate from step (3) to isomerization to form additional quantities of 2,3-, 2,6- and 2,7-dimethylnaphthalenes and (7) recycling the isomerizate to step (1) for fractionation together with said desulfurization product.

7. In a process involving hydrodesnlfurizing a gas oil fraction boiling mainly in the range of 440-520" F, and containing mainly monocyclic and dicyclic aromatic by} drocarbons including monomethyl and dinrethylnaphthalene, separating from the desulfurization product material containing alkylnaphthalene and subjecting such material to a dealkylation reaction at a temperature above 1000 F. to produce naphthalene, the steps for recovering 2,3-, 2,6- and 2,'7-dirnethylnaphthalenes as additional products which comprises; (1) distilling said desulfur'ization product to obtain three fractions boiling, respectiyely, in the approximate ranges of 500-509" F., 509513 F. and 513-520" R; (2) chilling the 500-509 P. fraction to a temperature sufliciently low to crystallize 2,6- and '2,7-dimethylnaphthalenes contained therein; (3) separat 'ing filtrate from the crystallized product; (4) chilling the 513-520 P. fraction to a temperature sufiiciently low to crystallize 2,3-dimethylnaphthalene contained therein; (5) separating filtrate from the crystallized 2,3-dirnethy1naphthalene; 6) subjecting a portion of the filtrate frorn step o (5) together with desulfurlzation product boiling below 500 F. to said dealkylation reaction to form naphthalene; (7) isomerizing the remainder of the; filtrate from step (5) together with said 509-513 l-"a tracti-on and the illtrate from step (3) to form additional qtia-ntities of 2,3-, 2,6- and 2,7-dimethylnaphtl1al enes;and (8 recycling the isomerizate to step (1) for fractionation together with said desulfurizationproductl References Cited by the Examiner- Suld etal, 260 -668 DELBERT E. GANTZ, Brimgry Examiner. ALPHONSO D. SULLIVAN, Examiner. 

1. PROCESS FOR PRODUCING 2,3-, 2,6- AND 2,7-DIMETHYLNAPHTHALENES FROM A HYDRODESULFURIZED GAS OIL AROMATIC CONCENTRATE INCLUDING AROMATICS BOILING IN THE RANGE OF 500-520*F. WHICH COMPRISES: (1) DISTILLING SAID CONCENTRATE TO OBTAIN THREE FRACTIONS BOILING, RESPECTIVELY, IN THE APPROXIMATE RANGES OF 500-509*F., 509-513*F. AND 513-520*F.; (2) CHILLING THE 500-509*F. FRACTION TO A TEMPERATURE SUFFICIENTLY LOW TO CRYSTALLIZE 2,6- AND 2,7DIMETHYLNAPHTHALENES CONTAINED THEREIN; (3) SEPARATING FILTRATE FROM THE CRYSTALLIZED PRODUCT; (4) CHILLING THE 513-520*F. FRACTION TO A TEMPERATURE SUFFICIENTLY LOW TO CRYSTALLIZE 2,3-DIMETHYLNAPHTHALENE CONTAINED THEREIN; (5) SEPARATING FILTRATE FROM THE CRYSTALLIZED 2,3-DIMETHYLNAPHTHALENE; (6) ISOMERIZING THE 509-513*F. FRACTION AND FILTRATES FROM STEPS (3) AND (5) TO FORM ADDITIONAL QUANTITIES OF 2,3-, 2,6-, AND 2,7-DIMETHYLNAPHTHALENES; AND (7) RECYCLING THE ISOMERIZATE TO STEP (1) FOR FRACTIONATION TOGETHER WITH SAID CONCENTRATE. 